I don't know of any actual serfs who kept memoirs. We do have fragmentary records from former serfs (such as letters, petitions, or resolutions by village soviets), although these were often recorded by others (e.g. a petition authored by a village assembly might be recorded by the local priest). In general though, we get our evidence of serfs's experiences from other sources.

The most obvious obstacle to serfs recording their memoirs is the fact that the overwhelming majority were illiterate. In the typical mir (commune) on an estate in central Russia, the only person with anything beyond the most elementary education would be the priest, and - if the local landowner lived on the estate rather than collecting rents in absentia - the local Lord and his sons. Thus, the interests of serfs are most often captured by officials writing about them or on their behalf. The literacy rate at the time on emancipation was about 15%. Before 1861, serfs were legally excluded from education without the express permission of their Lord, after 1861, they were excluded by imposing tuition fees which would prevent former serfs from gaining anything more than an elementary education.

Furthermore, we know from the later Bolshevik likbez (illiteracy eradication) campaigns that one of the biggest obstacles to ending illiteracy was cultural: even when elementary education was made free and compulsory in the 1920s, the Bolsheviks struggled to convince peasants of the value of education - peasants saw immediate economic advantage to having their children work the fields (especially at harvest time), and believed that honest work in the fields was better preparation for a life of work anyway. Thus, it wasn't until collectivisation under Stalin uprooted traditional village life from 1927 or so that the majority of rural children were actually attending school.

Thus, the closest we have to the authentic voices of serfs are the memoirs of the more socially mobile and ambitious of their children and grandchildren, who tended to possess much higher rates of literacy.

For example, Sergey Semyenov was born to former serfs in 1866, but due to the overcrowding and land shortages that followed emancipation, was forced to emigrate from his village in order to seek work. As a socially ambitious and economically itinierant worker, he eventually acquired the basics of an education. He made connections with populist and liberal writers who wanted to better understand peasant Russia and who in turn deepened his intellectual development. He took advantage of the Stolypin reforms to extol to his fellow peasants the need for reform from about 1908, then returned to the countryside as an evangelist for the Bolshevik cause after the civil war. Born the child of a serf, he became an accomplished writer is his own right. His writings give us a picture of a Russian peasantry that was deeply insular and resistant to outside forces, and totally unwilling to embrace economic reform.

Main sources: A People's Tragedy by Orlando Figes and Stephen Smith's An Empire in Crisis.